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Because of an oversight a part that has a footprint SOT89-ECB (PNP-BJT), ended up on my board, but when I tried to find a transistor that actually has compatible pin configuration I came out with nothing. So what is the point of even having a footprint like that in a standard library (I used Eagle, but when searching I found this footprint in other libraries as well)? Are there actually compatible parts that I did not find?

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  • \$\begingroup\$ It doesn't have to be a PNP \$\endgroup\$
    – DKNguyen
    Commented Aug 22, 2019 at 13:27
  • \$\begingroup\$ How about (say) a BCX53? This pinout doesn't seem to be overly unusual. \$\endgroup\$ Commented Aug 22, 2019 at 13:28
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    \$\begingroup\$ @RichardtheSpacecat BCX53 is the standard BCE layout the one I am after has the leads mirored (some datasheets have a bit confusing pinouts). \$\endgroup\$ Commented Aug 22, 2019 at 13:36
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    \$\begingroup\$ @DaveTweed More just a matter of interest, I wondered why it even exists, if someone happens to know specific part that would be a bonus, but I don't have high hopes for that. \$\endgroup\$ Commented Aug 22, 2019 at 13:38
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    \$\begingroup\$ @RichardtheSpacecat The BCX53 has the base on the left, emitter on the right when viewed from on top , leads towards you. This is the industry standard SOT89 bipolar pinout. = BCE. A ECB pinout may exist but I don't recall having seen one. BCX53 \$\endgroup\$
    – Russell McMahon
    Commented Aug 22, 2019 at 13:59

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... a part that has a footprint SOT89-ECB (PNP-BJT), ended up on my board, but when I tried to find a transistor that actually has compatible pin configuration I came out with nothing. So what is the point of even having a footprint like that in a standard library ... Are there actually compatible parts that I did not find?

The footprint may be useful for an XC6372 - your brain may need a second or two to recalibrate when 1st looking at that page :-).

The BCX53 has the base on the left, emitter on the right when viewed from on top , leads towards you. This is the industry standard SOT89 bipolar pinout. = BCE.

Data sheets like this one may mislead you - until it is realised that they have (stupidly) shown a bottom view. SOME sellers advertise this as ECB pinout eg this page shows it as ECB - but they are wrong.

"BEC" !!!- SXA289 - admittedly for good reason :-).

The fact that the "strange" BEC configuration exists for the SXA289 (see above) MAY provide an answer. The 289 is designed as a stripline RF amplifier with central emitter grounded and signal passing symmetrically across the component - hence BEC. It could equally have been CEB.

It is conceivable that in some niche circuits it is advantageous for complementary parts to have either bases or emitters physically adjacent. So a ECB-BCE or BCE-ECB arrangement might then make sense.

Using FETs rather than bipolars a contrived example is two FETs of the SAME type but with opposite pinout being arranged adjacently to provide a GDS-SDG arrangement (equivalent to bipolar BCE-ECB) with sources joined AND gates joined. You now have a back to back/series opposed pair that acts as a bidirectional switch when Vgs is applied to turn on both transistors at one (each operating in different quadrants!).

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  • \$\begingroup\$ I notice you're talking about the emitters and bases of FETs; I think you probably mean sources and gates? \$\endgroup\$
    – Hearth
    Commented Jun 18, 2020 at 11:32
  • \$\begingroup\$ @Hearth Thanks. Edited. That's what I get for turning old comments into an answer :-). \$\endgroup\$
    – Russell McMahon
    Commented Jun 19, 2020 at 0:53

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